The present invention relates to an optical switch device making use of an optical material which varies in refractive index with the variation of temperature, and more particularly to an optical switch device which is suited to light beams of multimode.
Change-over control for light beams has heretofore been practiced with use of a material having opto-electric effect or opto-magnetic effect. An electric field or magnetic field is applied to an optical waveguide layer made of such a material to vary the refractive index of the layer and thereby change the direction of propagation of a light beam travelling through the layer. However, the optical switch device of this type is usable only for light beams of single mode propagating through an optical waveguide layer which is about 2 to about 5 .mu.m in thickness or depth because the electric field or magnetic field attenuates to a greater extent with increasing depth from the surface of the material inward and also because a very high voltage or great current is required for generating an electric field or magnetic field sufficient for deflecting light beams over a depth of more than 200 .mu.m. There is another problem. While the optical waveguide layer is formed by thermally diffusing an impurity substance into a dielectric material from its surface which material has an opto-electric effect or opto-magnetic effect, it is extremely difficult to form in the dielectric material a multimode optical waveguide layer having a thickness of more than 200 .mu.m.